U.S. military aid program begun during World War II. Designed originally as a means for the United States to assist Great Britain without becoming a belligerent itself, the Lend-Lease program provided more than $50 billion in aid to 38 nations between March 1941 and June 1947. The British Empire received the most aid under the program ($31.4 billion), followed by the Soviet Union ($11 billion).

The immediate impetus for Lend-Lease was the fall of France in 1940, which left Great Britain fighting Adolf Hitler alone. Strapped for cash, Britain could no longer afford to purchase supplies from the United States. Britain's economic crisis notwithstanding, President Franklin D. Roosevelt believed that the United States had to find ways to maintain the resolve of the British, thereby allowing them to continue in the war.

British problems were not the only barrier to be overcome. U.S. firms were hampered from trading with Britain because of restrictions included in the Neutrality Acts that were passed in the late 1930s. These measures required that trade be conducted on a "cash-and-carry" basis, meaning that American firms could neither extend credit nor transport materials across the U-boat–infested Atlantic Ocean. With Britain nearly out of hard currency, trade under the cash-and-carry provisions became virtually impossible. The original Lend-Lease authorizations specified that the funds were to be given only to democracies that agreed to pay the loans back in full at the earliest possible opportunity.

From the start, however, Roosevelt envisioned that Lend-Lease would operate much like his domestic New Deal did. It would be a practical and flexible program that was able to meet changing demands. It would also be centrally controlled from the executive branch, leaving Roosevelt the options of deciding which nations would receive aid and what forms that aid would take. Rhetoric notwithstanding, the program was more realistic than ideological.

Yet Lend-Lease was not an entirely idealistic endeavor. Roosevelt also promoted it as being in the direct strategic interests not only of Great Britain but also of the United States. He compared Lend-Lease to lending a neighbor a fire hose when his house was in flames. This act would help save the lender's house from destruction as well, and once the fire was out, the hose would be returned.

To answer the charge of critics who believed that the impoverished British government would never repay Lend-Lease obligations, Roosevelt said that he expected Britain to honor a gentleman's agreement to eventually repay the United States in kind. He linked Great Britain's war to the United States in compelling rhetoric that helped to overcome abiding strains of American isolationism. Roosevelt reinforced these points in a series of "fireside chats" that led to widespread public acceptance of the program.

On 6 January 1941, supporters introduced the Lend-Lease bill, which they patriotically numbered H.R. 1776, in Congress. In a speech delivered soon afterward, Roosevelt connected Lend-Lease to the famous Four Freedoms that defined America's global goals: freedom of speech, freedom of religion, freedom from want, and freedom from fear. Lend-Lease, Roosevelt argued, promised to further those aims without putting American lives at risk. After adding an amendment stipulating that the U.S. Navy would not convoy supplies to Britain directly, the bill passed both houses of Congress by large majorities on 8 March 1941. It authorized the president to "sell, transfer to, exchange, lease, lend, or otherwise dispose of" property to any nation whose defense the president deemed "vital to the defense of the United States." As the program's success became more manifest, public opposition to Lend-Lease, always in the minority, became even less vocal.

The emergency faced by the Soviet Union after the German invasion of June 1941 required a reconsideration of the specific provision that Lend-Lease applied only to democracies. In August, Roosevelt had declared that Lend-Lease did not apply to the Soviets, but he was even then accepting a 29-page list of Soviet requests. Despite serious misgivings from anti-Communist members of Congress, where the extension was debated over a four-month span, the United States finally added the Soviet Union to the program in November 1941. Roosevelt agreed with British Prime Minister Winston L. S. Churchill that, whatever the ideological conflict, the Soviets had to be supplied if they were to remain in the war against Germany. Sensitive to the tensions involved in extending Lend-Lease aid to a Communist nation, Roosevelt sent Harry Hopkins, his most trusted adviser, to Moscow to coordinate Lend-Lease assistance there.

The U.S. Office of Lend-Lease Administration worked to overcome myriad complex problems of logistics. Until the Allies gained the upper hand in the Battle of the Atlantic, supplying Britain proved difficult, and supplying the Soviet Union necessitated air routes over Africa, sea routes along the Arctic Ocean, and land routes across Persia. Complications with flying supplies over "the Hump"—as the Himalaya Mountains were known—limited U.S. aid to China, though that country still received almost $2 billion in assistance. Because of the immense logistical difficulties, the vast majority of Lend-Lease aid to China comprised light weapons systems that could be flown in.

Lend-Lease worked in reverse, as well. Thus, Britain shared with the United States radar technology, in which it then led the world. The British also provided technology on jet engines and rocketry. Reverse Lend-Lease of all types amounted to some $7.8 billion during the war.

Lend-Lease provided a wide range of arms, equipment, food, and raw materials to nations fighting the Axis powers. In the end, munitions formed almost half of the total aid package. Although the British Empire received more than 60 percent of the aid distributed under the program, Lend-Lease assistance proved to be critical to the Soviet Union. The Americans provided the USSR with 34 million sets of uniforms, 15 million pairs of boots, 350,000 tons of explosives, 3 million tons of gasoline, sufficient food to provide a half pound of food per Soviet soldier a day, 12,000 railroad cars, 375,000 trucks, and 50,000 jeeps. American vehicles and petroleum supplies allowed the Red Army to develop a "deep-offensive" doctrine in 1943 that enabled Soviet units to go greater distances. The Soviet Union could also concentrate on the production of tanks and artillery because of the steady supply of trucks and jeeps arriving from the United States.

Roosevelt and his closest advisers sought to employ Lend-Lease to open the Soviet system to American ideas. In a similar vein, they insisted that any nation receiving Lend-Lease assistance had to agree to open its markets to U.S. products. Thus, Washington finally forced Great Britain to abandon the Imperial Preference System that had provided more favorable trade terms to members of the British Empire.

Lend-Lease paid important dividends on the strategic level, as well. U.S. aid helped to fend off Soviet demands for a second front in western Europe. It also helped the Americans to convince Chinese Generalissimo Jiang Jieshi (Chiang Kai-shek) that he must at least appear to accept the counsel of his American advisers—most notably, the reform-minded Lieutenant General Joseph W. Stilwell. The United States later extended Lend-Lease aid to many Latin American nations, prominently Mexico and Brazil. The program brought these nations closer to the Allies and ensured that the Axis powers would not be able to establish important connections there.

Lend-Lease thus served many key roles during the war. Most critically, it unquestionably shortened the conflict and relieved the suffering of millions. As Allied armies advanced across western Europe, Lend-Lease funds paid for food and livestock shipments to France, the Netherlands, and Belgium. America's allies certainly appreciated its value. Churchill called Lend-Lease the most unsordid act in history. Although Soviet historians later discounted its value, Joseph Stalin himself said that the Soviet Union could not have won the war without Lend-Lease.